The present invention relates to a test system for an electromagnetic trailer brake system. More particularly, the present invention relates to a test system that can indicate the condition of an electromagnetic trailer brake system.
Test systems for electromagnetic trailer brake systems of the above-mentioned general type are known in the art.
U.S. patent application Ser. No. 658,459 to Myers, filed Feb. 17, 1976 and as disclosed in U.S. Pat. No. 4,066,996 to Davis, relates to breakaway protection for electrically controlled trailer brakes.
Myers teaches a voltage indicator with which the driver may test the auxiliary trailer battery to determine not only whether the battery has sufficient voltage to initially energize the brake coils but also whether the battery has adequate storage capacity to hold such voltage and keep the coils safely energized for a sustained period during breakaway. If the auxiliary trailer battery is good, the voltage indicator provides the driver with a visual signal informing him or her that it if safe to tow the trailer. Unfortunately, inherent in this design, the voltage indicator can also provide a safe signal by reason of, for example, an interruption of the excitation circuit to the brake coils or the loss of one or more of the coils from the circuit.
U.S. Pat. No. 4,066,996 to Davis teaches an improvement over the patent application of Myers, described supra, and assigned to the same assignee.
The teachings of Davis prevents the voltage indicator from producing a safe test signal unless all of the brake coils are properly connected in the excitation circuit and are all capable of receiving excitation current from the auxiliary trailer battery. Furthermore, the teachings of Davis detects whether all of the brake coils are capable of receiving excitation current by sensing the magnitude of the current in the excitation circuit and by disabling the voltage indicator unless the magnitude of the current through the circuit is sufficiently high to establish that all of the coils are in fact drawing current. This determination is achieved by comparing the current through the circuit to a predetermined threshold value.
However, the voltage indicators of both Myers and Davis test the output of the auxiliary trailer battery utilized only during breakaway and do not test the output of the towing vehicle battery utilized during normal towing for energizing the electromagnetic trailer brakes.
U.S. Pat. No. 3,840,276 to Jubenville relates to a control circuit for automatically monitoring and checking out a trailer brake system.
Jubenville teaches a safety or warning light which indicates if a supplementary portion of a vehicle braking system is inoperative. Furthermore, Jubenville teaches an electrical trailer braking system adapted to control oscillations or swaying of the trailer relative to the towing vehicle. Jubenville's warning light monitors only the oscillation controlling portion of the braking system and does not indicate whether the basic trailer braking system is operative, nor does Jubenville provide means for selectively testing the operability of portions of the basic trailer braking system.
U.S. Pat. No. 4,122,434 to Jensen relates to a test system for trailer brake mechanism and teaches an improvement over the aforementioned patent to Jubenville.
Jensen teaches an electrical testing circuit that indicates to the towing vehicle operator that the towed vehicle braking system is electrically operative. Furthermore, the electrical testing circuit selectively tests certain portions of the electrical braking system to more readily locate malfunctioning components. However, Jensen's warning or monitoring lamp monitors only the electrical conductivity of various portions of the electrical braking system and does not indicate if the electrically conductive braking system contains sufficient current to successfully stop the trailer.